Sanctions aren't the answer. If Washington is serious about building a new economic and security architecture across South and Central Asia, it can’t avoid working with Iran.

Speaking last September on the sidelines of the U.N. General Assembly, Secretary Hillary Clinton articulated the U.S. government’s vision of a "New Silk Road" running through Afghanistan. In a throwback to the circuit that once connected India and China with Turkey and Egypt, she argued in favor of a network of road, rail, and energy links that would traverse Central Asia and enable Turkmen gas to fuel the subcontinent’s economic growth, cotton from Tajikistan to fill India’s textile mills, and Afghan produce to reach markets across Asia.

By enhancing economic integration, the strategy aims to boost local economies and stabilize the region. There are certainly doubts about the plan’s feasibility. But at least, after years of endlessly repeating the myth that Afghanistan is the "graveyard of empires," this new Silk Road recognizes that, from the times of the ancient Persians to Alexander the Great, and through the Mongols, Mughals, and Sikhs, Afghanistan was at the center of global exchange.

This effort has the dual benefit of distributing the Afghan burden away from Pakistan, which has long been America’s only link to Central Asia. For decades, Washington’s dependence on Islamabad has amounted to U.S. support for a Pakistani military-economic complex that has played a bloody double game in Afghanistan, uses terrorists and militants as strategic weapons, and has proven the world’s most flagrant nuclear proliferator. And it’s working: By late 2011, increased use of the Northern Distribution Network (NDN) through Central Asia shifted NATO’s dependence on Pakistan from bearing nearly 70 percent of its supplies and fuel in previous years to less than 30 percent today. But the NDN comes with pitfalls of its own, giving Russia and Kyrgyzstan increased leverage over U.S. supply lines, forcing the United States to turn a blind eye to unsavory dictators in Uzbekistan and Tajikistan, and costing three times more than shipping from the Arabian Sea.

Yet there is an important stretch of this new Silk Road that is conspicuously overlooked: Iran. Because Iran lies strategically between Mesopotamia, Anatolia, the Caucasus, the Caspian Sea, Central and South Asia, the Persian Gulf, and the Arabian Sea, a broader network of trade is nearly impossible without it. Even the original Silk Road had Persia as a central pillar, including the key trading posts of Gedrosia in modern Baluchistan, Hecatompylos in today’s Semnan Province, and Traxiane, currently Khorasan province.

Today, the Iranian "Eastern Corridor" in particular has the potential to reshape Afghanistan’s strategic future. Constructed by India in September 2008, the road passes from Chabahar Port on the Arabian Sea through Iran’s relatively stable Sistan-Baluchistan and Khorasan provinces, and onward to the town of Milak on the Afghan border. From there it connects with the Indian-built Zaranj-Delaram highway in western Afghanistan’s Nimruz Province, which subsequently links to the Afghan Ring Road. New Delhi, Tehran, and Kabul have planned a railway line along the entire route to facilitate trade — particularly of Afghanistan’s estimated $1 trillion in minerals — to and from Central Asia. New Delhi — like Ankara and others — is coming up with "creative" ways to engage with Iran while insulating itself from punitive action by the United States, including building new, independent corporate entities that do not participate in Western markets.

At 135 miles, the Chabahar road to the Afghan border is far shorter than the nearly 1,100-mile trip from Karachi to the Torkham border in northeastern Pakistan, and even shorter than the 500 miles from Karachi to the Chaman border in northwest Pakistan. Thomas Barfield, author of the comprehensive Afghanistan: A Cultural and Political History, puts it succinctly: the "new transport corridor" through Chabahar "ends Pakistan’s monopoly on seaborne transit trade to Afghanistan … [making] Iran the most efficient transit route into Central Asia."

In contrast to the zero-sum logic that defines the current escalation of tensions between the United States and Iran over the Islamic Republic’s nuclear program, the two countries share substantial interests in increasing regional trade and stability. Tehran hopes to stabilize Afghanistan and export its own natural gas and petroleum — 16 percent and 10 percent of the world’s total reserves, respectively — to the world. Indeed, its existing infrastructure — albeit in need of much improvement — is better suited to bring Turkmen natural gas to market than alternate plans to construct new pipelines across Afghanistan, Pakistan, and India, or all the way through the Caspian, Caucasus, and Turkey.

However, Washington so vehemently sought to shut Tehran out of any regional plans that it even preferred to endorse the Taliban in an effort to stabilize and develop energy pipelines through Afghanistan in the mid-1990s. At the time, Iranian Deputy Minister of Oil Ali Majedi stated, only slightly hyperbolically, "the total cost for [shipping Central Asian hydrocarbons through] Iran would be $300,000. How does that compare with [well over] $3 billion for a pipeline through Turkey?"

Cooperation between Washington and Tehran on economic matters seems exceptionally unlikely these days. In fact, the United States is pushing for more sanctions, not more interaction. But Iranian and U.S. political goals in Central Asia are not necessarily in conflict: Within Afghanistan, the militantly Sunni Taliban that threatens the West is similarly anathema to Shiite Iran — Iran’s alleged tactical support is decidedly driven by anti-American rather than pro-Taliban motives.

Despite U.S. attempts to isolate Tehran, countries like India, China, Turkey, and Russia are banking on Iran for the long haul, precisely because it is a relatively stable, energy-rich geographic lynchpin. With emerging projects like an Iran-Pakistan-China gas pipeline, an Economic Cooperation Organizationrailway from Istanbul to Tehran and Islamabad, and the North-South Trade Corridor, Iran’s regional influence is inevitable. The United States may as well adapt itself to that fact while it is still engaged in the region.

And yet, engagement with Iran is a virtual heresy in Washington. The discussion in the U.S. capital is focused on a renewed campaign of ever-tighter sanctions, and militaristic rhetoric from the nation’s top officials is paving not a silk road, but a warpath.

Ratcheting up war pressure simply strengthens Tehran’s drive to get the bomb, increases regional instability, and drives up energy prices in the midst of a recession. Only concerted diplomacy will yield mutually beneficial shared interests, including cooperation in Afghanistan and Iraq — something Tehran had delivered in the wake of the invasions — and a fully functioning New Silk Road.

Of course, the story goes that diplomacy did not even work when President Barack Obama "extended a hand" to Tehran in mid-2009. But as Trita Parsi describes in his book A Single Roll of the Dice, diplomacy with Iran actually did not fail at all; it was abandoned due largely to domestic political concerns. Key among them were objections from Saudi Arabia, Israel, and their supporters in the United States, who "fear[ed] that a thaw in U.S. relations with Iran would come at the expense of America’s special friendships" with both states.

Washington needs to decide how many more terrorists must be bred, and troops, dollars, lives, and years expended along the Durand Line to keep validating this perception. As Brazil, Turkey, India, China, and the rest of the world work to capitalize on Iran’s undeniable potential, it would serve the United States well to follow their lead.